1. Field of the Invention
The present invention relates to a signal receiving apparatus, a signal receiving method, a signal receiving program and a signal receiving system. More particularly, the present invention relates to a signal receiving apparatus producible at a low cost, a signal receiving method adopted by the signal receiving apparatus, a signal receiving program implementing the signal receiving method and a signal receiving system employing the signal receiving apparatus.
2. Related Art of the Invention
In a tuner which receives a high-frequency signal and fetches only a signal having a desired frequency assigned to typically a broadcast station from the high-frequency signal, it is necessary for a tuned circuit employed in the tuner to serve as a circuit for filtering the high-frequency signal to have its tuning center frequency match the desired frequency referred to as a reception frequency. For more information on this, the reader is advised to refer to documents such as Japanese Patent Laid-open No. 2008-259269 (FIG. 13). Thus, for a tuner employed in a TV (television) receiver or the like, a work to adjust a tuned circuit thereof is carried out in order to change the tuning center frequency of the tuned circuit to a value matching the reception frequency. In this specification of the present invention, the tuning center frequency of a tuned circuit is also referred to as a resonance frequency of the tuned circuit.
For example, there is a method by which the capacitance of a capacitor employed in a resonance circuit serving as a tuned circuit is adjusted prior to shipping of the tuner from the factory and capacitances obtained as a result of the adjustment are stored in a NVM (Non-Volatile Memory). In accordance with this method, the work to adjust the tuned circuit is carried out prior to the shipping as follows. First of all, a signal generator used for the capacitance adjustment is driven to generate a signal having a frequency set at a value equal to the reception frequency of an input signal received by the tuner serving as the object of the adjustment and supply the signal to the tuner. Then, the capacitance of the capacitor employed in the resonance circuit employed in the tuner is adjusted to detect a capacitance value which maximizes the level (or the amplitude) of an IF (Intermediate Frequency) signal output by a mixer circuit also employed in the tuner. Subsequently, the capacitance value is stored in a nonvolatile memory as an adjusted value. When a broadcast signal is actually received in the field, the adjusted value is read out from the nonvolatile memory to be used as a capacitance for setting the resonance frequency of the tuned circuit at the reception frequency in an operation to control the capacitance of the capacitor.
In addition, there is also a tuner including an embedded signal generator used for the capacitance adjustment. In the case of such a tuner, a capacitance adjustment work is carried out in the field as an initial operation when a broadcast signal is actually received. The capacitance adjustment work used to be done prior to shipping of the tuner from the factory to adjust the capacitance and detect the adjusted capacitance value.